Web roll cradle with positive drive

ABSTRACT

Apparatus and method of cyclic or intermittent feeding and unwinding of sheet material includes a pneumatic motor that drives the rotary web roll support and a brake that serves to stall out the motor when the predetermined length of material has been unwound. Draw means is provided to draw the predetermined length of film in a manufacturing process, such as packaging, with a slack loop being formed between the draw means and the web roll. The pneumatic motor is preferably a cylinder and rack combination with a drive stroke producing a capability greater than said predetermined length with the brake stalling out the motor at the end of the stroke to assure proper feed during each cycle and to maintain the tension in the web at a minimum and substantially constant during the complete operation. The slack loop is formed by a dancer assembly with linkage means comprising a cam and leaf spring applying the brake in a progressive manner only during the final moments of unwinding of the material. The dancer assembly desirably has insufficient pulling or tensioning power to pull film from the web roll so that complete reliance for feeding is put on the positive drive. The drive means and the draw means are operated at mutually exclusive times and are coordinated by first and second valves that actuate the drive means as the draw means are withdrawn to complete the drawing step.

United States Patent [1 1 Henry 1*Nov. 25, 1975 WEB ROLL CRADLE WITHPOSITIVE DRIVE [75] lnventor: Nelson R. Henry, Decatur, Ga.

[73] Assignee: The Woodman Company, Inc., Decatur, Ga.

[ 1 Notice: The portion of the term of this patent subsequent to Jan.22, 1991, has been disclaimed.

[22] Filed: Jan. 21, 1974 [21] Appl. No.: 435,246

Related US. Application Data [63] Continuation of Ser. No. 234,494,March 14, 1972,

Pat. No. 3,787,00l.

Primary ExaminerEdward J. McCarthy Attorney, Agent, or Firm-Lowe, King &Price TO PKG. MACH.

[57] ABSTRACT Apparatus and method of cyclic or intermittent feeding andunwinding of sheet material includes a pneumatic motor that drives therotary web roll support and a brake that serves to stall out the motorwhen the predetermined length of material has been unwound. Draw meansis provided to draw the predetermined length of film in a manufacturingprocess, such as packaging, with a slack loop being formed between thedraw means and the web roll. The pneumatic motor is preferably acylinder and rack combination with a drive stroke producing a capabilitygreater than said predetermined length with the brake stalling out themotor at the end of the stroke to assure proper feed during each cycleand to maintain the tension in the web at a minimum and substantiallyconstant during the complete operation. The slack loop is formed by adancer assembly with linkage means comprising a cam and leaf springapplying the brake in a progressive manner only during the final momentsof unwinding of the material. The dancer assembly desirably hasinsufficient pulling or tensioning power to pull film from the web rollso that complete reliance for feeding is put on the positive drive. Thedrive means and the draw means are operated at mutually exclusive timesand are coordinated by first and second valves that actuate the drivemeans as the draw means are withdrawn to complete the drawing step.

7 Claims, 5 Drawing Figures H CONTROL x I T smzr E :Q- l DRAWING PHOTOCELL 1 ONE WAY CLUTCH BRAKE ON sconce ONE WAY CLUTCH A5 FILM l5 f muwuDANCER rtottsds MOVE 80 uP-. I

T0 PKG. MACH. CONTROL CONTROL NR PRESSURE SOURCE 9 CON 0L oV Puoro CELLas US. Patent Nov. 25, 1975 SheetlofZ 3,921,928

TO PKGMACH. I "x o CONTROL w awn PHOTO can 1 \s W ONE WAY CLUTCH 3 G '15W b A 2 b 52, 7 p 19 b7 A$ HLM l T 1 In DRAWN, omcaz l BRAKE ROLLERSMOVEI 5| ON 0 4O so M 54 ,1 J MAN 56 TI 1 71 I] DRWE 51 "le =5 W 2%/ T\/A\\.VE\

10 as 81 "/9 7M 75/5 I l m2 as T256 8 W 5 PBESSURE 91- .4%%H.

cameos.

FROM w PHO o 9 T cat 93 ONE WAY CLUTCH MNQTER ESSEEE wemcu CONROL 9'1. 4

Elev

PHOTO CELL 95 US. Patent Nov. 25, 1975 Sheet20f2 3,921,928

WEB ROLL CRADLE WITH POSITIVE DRIVE This is a continuation ofapplication Ser. No. 234,494, filed Mar. 14, 1972, now US. Pat. No.3,787,001.

The present invention relates to unwinding of sheet material, such aspackaging film, and relates more particularly to a system for unwindingmaterial by positive drive of the web roll and maintenance of aconstant, minimum tension in the web.

BACKGROUND OF THE INVENTION In form and fill packaging, as in many otherenvironments where a web of sheet material is handled, it is necessaryto withdraw predetermined lengths of material from a web roll. Thelength of film drawn from the roll is then used for forming a packagefor a commodity, or for some similar operation. It is necessary in suchoperations to maintain the lengths of sheet material or film of an exactdimension and to draw the film without unduly tensioning the sheetmaterial. The first requirement of drawing exact lengths of material hasbeen satisfactorily met for all grades, thicknesses and types of sheetmaterial, such as by use of photoelectric control responsive to apreprinted mark on the film at each package length. This photocellcontrol is integrated into the overall packaging machine control andexact lengths of material or packaging film may be drawn in a continuousfashion without difficulty.

However, with regard to the latter problem related to the actual feedingand unwinding of the sheet material, some difficulty today still exists.First, there are many types of film that are used in packaging machinesso that in order for a machine to be versatile it must be capable ofoperating on different films that vary greatly in terms of resistance tounwinding, stretchability, fracturability and general strength. In thepast, unwinding systems have almost exclusively relied upon the use ofthe tension in the web generated by the drawing means to pull thematerial from the roll which is supported on a rotary support means,either on an arbor or a web roll cradle. The rotary support means isbraked at the end of the drawing stroke by means ofa dancer arm that isresponsive to the decrease in tension of the web in a slack loop. Inother words, the sheet material is pulled from the web rool by anincrease in tension in the web; this increase in tension decreasing thesize of the slack loop by raising a dancer arm. The connected brakemeans is taken out of operative engagement with the rotary support meansand the spring bias of the dancer arm increases the tension in the filmto, in turn, start the web roll turning for unwinding. Upon completionof the feeding, the roll will continue to turn until the dancer arm onceagain applies the brakes by another decrease in tension; that is, anincrease in the size of the slack loop. Such a prior art system that issuccessful with most kinds of packaging material are shown in myprevious patents Henry et al., entitled Web Roll Cradle, issued Sept. 9,1969, US. Pat. No. 3,465,979 and Henry, entitled Web Roll Cradle forLoosely Wound Material, issued Feb. 9, 1971, US. Pat. No. 3,561,692.

One particular type of packaging film that is becoming more and morepopular in the form and fill environment, is polyethylene film. Thisfilm is preferred in many packaging situations, such as for frozen foodsand other commodities, such as nuts and candies, because of its softnessand highly pliable nature. These qualities however, make it extremelydifficult to use the tension in the film itself to pull the materialfrom a web roll in a successful manner. The successive turns of the filmon the web roll tend to stick to each other under certain ambientconditions, such as in a hot and humid environment, and the web issubject to stretching when placed under tension.

Furthermore, with all kinds of packaging film in roll form, there is theproblem of inadvertently dropping and/or resting a roll on its side.This forms a deleterious flat spot on the periphery of the roll. If acradle is used, the support rollers tend to stall due to wedge-likeaction when the spot engages either roller. Also, the adjacent turns ofthe web are pressed together at the spot and thus tend to stick morethan usual during unwinding. These conditions thus prevent efficientunwinding, either on a cradle or arbor, by the previous web pull ortensioning method. Finally, the size of the web roll previously has beenlimited since the considerable inertia that must be overcome to start anoversized roll is greater than can be supplied by pulling on the webwithout damage thereto.

OBJECTIVES OF THE INVENTION And, accordingly, it is the main object ofthe present invention to provide a universal feeding and unwindingsystem for sheet material from a web roll wherein positive drive isprovided directly to the web roll and the tension in the web ismaintained at a minimum and substantially constant.

It is still another object of the present invention to provide anunwinding system wherein a predetermined length of material may be fedfrom a web roll without reliance on the tension in the material forcontrol.

It is still another object of the present invention to provide anunwinding method and apparatus in conjunction with a drawing of apredetermined length of material for packaging film that operates on theconcept of providing overdriving capacity directly to the web roll and abrake system responsive to a slack loop that overrides or stalls out thedrive after a predetermined length of material has been unwound.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT My present invention ispreferably embodied in a web roll cradle wherein the roll supportrollers are positively driven directly in response to a function otherthan the tension in the web being drawn from the roll. By tieing thecontrol of the positive drive on another function, such as thecompletion of the drawing stroke of the sealing jaws of a form and fillpackaging machine, the web is not subject to deleterious stretching,fracturing or tearing that has been a problem in the past especiallywhen certain packaging films are used. The system is highly versatilebecause of this feature, is smoother in operation and highly reliable.This system can be used not only for any type of packaging material, butalso in virtually any application other than packaging machines whereintermittent unwinding is a necessity.

The positive drive is preferably provided by a pneumatic cylinder havinga drive rack connected to the piston and operating through a gear trainand one-way clutch to drive the support rollers of the cradle. Theactuation of the cylinder is controlled to feed a new length of filmfrom the web roll by the packaging machine control including thephotocell detector that interrupts the drawing of the film by thesealing jaws. In

this manner, the initiation of the drive cycle is independent of thetension, and yet is invariably in step with the needs of the machine. Oneach cycle of the machine, the pneumatic cylinder has sufficientcapacity to unwind more than a single, predetermined length of materialin order to assure that a shortage does not exist. The exact length offilm is obtained in a novel manner by employing a dancer assemblycontrol brake that serves to stall out or override the pneumatic motorwhen the proper length has been unwound. A slack loop formed between theweb roll and the draw means controls the dancer with the maximum slackloop being provided at the start of the drawing step and the minimumslack loop being provided at the start of the driving step.

Further in accordance with the present invention, a linkage means in the.form of a cam and leaf spring is provided between the dancer assemblyand the brake in order to progressively apply the braking pressure inthe last moments of each unwinding step and to assure a rapid andpositive stop without virtually any increase in tension in the web.Although a conventional arbor can be used in accordance with the broaderaspects of the present invention, a roll cradle is preferred so that thedrive stroke is the same regardless of the diameter of the web roll. Thesystem automatically adapts to drawing different lengths of film over alimited range through the extra driving capacity since the brake meansor disabling means would merely override the driving motor at an earlieror later point, as required.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein I have shown and described only thepreferred embodiment of the invention, simply by way of illustration ofthe best mode contemplated by me of carrying out my invention. As willbe realized, the invention is capable of other and differentembodiments, and its several details are capable of modification invarious obvious respects, all without departing from the invention.Accordingly, the drawings and description are to be regarded asillustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of thefeeding and unwinding system of the present invention showing the webroll cradle in a standby position and the draw means ready to draw a newpredetermined length of packaging film;

FIG. la is a schematic view of the feeding and unwinding system of FIG.1 showing the web roll cradle being driven after the completion of thedrawing step;

FIG. 2 isa side view of the system of FIG. 1 but showing the componentsin the sequence at the end of the cradle driving stroke and prior to thenext cycle;

FIG. 3 is a rear view of the web roll cradle taken in the directionshown by the line 3-3 of FIG. 2; and

FIG. 4 is a perspective view, enlarged to show detail, of the brake shoeand the operating linkage means on the dancer arm assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now toFIG. 1 of the drawings, a more detailed description of what I considerat present to be a preferred embodiment of the invention is shown inschematic form and the salient features may be more fully described. Thefigure essentially shows the feeding 7 system for the packaging film ofa form, fill and packaging machine, which comprises generally a packageforming device 10 and a web roll cradle 11 with a web W being inreadiness for unwinding and feeding from a web roll R. As mentionedabove, it will be readily understood by those skilled in the art thatthe broadest aspects of the invention are concerned with the novel jmanner of handling the web W and unwinding the same in an intermittentfashion from the rollR and that therefore the concepts could be used inenvironments other than packaging where intermittent draw-out of film orother sheet material is necessary.

The packaging forming device 10 may be of any con-f ventional structuresuitable to draw a predetermined length of material in an intermittentor cyclic fashion. In the embodiment shown, the predetermined length offilm or web W to be drawn during each cycle is represented by the lengthof package P formed by successive heat seals transversely positionedacross a tube T formed of the web W. These heat seals are formed bycooperating sealing jaws 15, 16 that are operated; toward and away fromthe tube T by a pair of air cylinders 17, 18. The cylinders 17, 18 arecarried on a reciprocating carriage 19 that is moved through anysuitable power means, such as a crank 20 and arm 21 driven from the maindrive of the packaging machine. Of

course, if desired, the relative movement between the tube T and thecarriage 19 alternatively may be ob tained by reciprocating a componentin engagement.

with the tube T while holding the carriage 19 in a fixed I position, asis well known. With reference to FIGS. 13, the main componen of the webroll cradle 11 may be more fully understood. The web roll R is supportedbetween a pair of support rollers 25, 26 which are coupled for mutualrotation by a suitable chain and sprocket coupling 27. Positionedoutboard of the chain sprocket on support shaft 28 of 1 I the rearroller 26 is a power gear 29 (see FIG. 3), which gear forms a part of agear train also including a driving step-up gear 30 mounted on a stubshaft 31 supported on the side frame F of the cradle 11. Formed as anintegral part of the power gear 29 is a one-way clutch33 A that permitsrotation of the driving gear in. a direction to unwind the web W fromthe roll R but slips when the gear is driven in the reverse direction.

The step-up gear 30 is driven from a drive rack 40 that is urged intoengagement with the smaller of the two gears by a guide roller 41, asshown in FIG.2. The

rack is attached to piston rod 42 of the pneumatic cylinder 43. Thus, asis apparent and as will be further explained, the actuation of thecylinder '43 operates to drive the web roll support rollers 25 26 in aforward direction to feed the web W with the one-way clutch 331permitting the return stroke in readiness for the next I c feedingcycle.

The web W passes around suitable stationary guide rollers 50 wheremultiple slack loops S and S2 are rear of the cradle assembly 11.

The rear end of the arms 52, 53 carry cam rollers 55,

56 that serve as a part of an operating linkage means to brake shoes 57,58 operating against circumferential friction surfaces 59, 60 at theends of the rear roller 26. I

As best shown in FIG. 4, the brake shoe 58 is mounted on a shaft 65extending outwardly from the side frame F and includes a suitablefrictional padding 66 that engages the brake surface 60 to bring aboutthe braking effect. A leaf spring 67 is fixed to the back of the brakeshoe 58 at the upper portion of a curved base 68. The spring 67 providesresiliency in the operation of the brake shoe 58 toward the brakingsurface 60 since the operating cam roller 56 engages the shoe 58 onlythrough the spring 67.

When the dancer arm assembly is in the raised position (see FIG. la),the brake shoe 58 is spaced from the cooperating surface 60 and thusthere is no braking force applied to the support roller 26. However,when the dancer arm assembly is in the lowered position of FIG. 1 (seealso FIG. 2) the brake shoe 58 is applied with maximum force due to thecamming action of the roller 56 against the spring 67. With the dancerarm assembly in its lowermost position, the leaf spring 67 is bent undermaximum conditions and the inside face thereof has been brought intoengagement with the curved surface 68 (see FIG. 2) to a point 69(FIG. 1) below the initial or attachment point (FIG. 2). This means thatthe leverage against the brake shoe 57 is progressively increased andthus the braking force is progressively increased to a maximum during,and only during, the final moments of downward movement of the dancerarm assembly. This gives a positive braking action that assures positivestalling out of the motor or cylinder 43 with a desirably rapid andprogressive but smooth deceleration motion. It will be understood thatthe operation of the brake shoe 57 at the far side of the cradle 11 isidentical and complementary to that just described.

The interconnected control between the package forming device and theweb roll cradle 11 forms an important aspect of the present inventionand will now be discussed. The pneumatic cylinders 17, 18 that operatethe sealing jaws 15, 16 are provided with pressurized fluid andexhausted through feed lines 70, 71, respectively. A first valve 72distributes the pressurized air from a feed conduit 73 to the line 70when the sealing jaws l5, 16 are to be moved toward the tube T that isbeing sealed to form the package P. Simultaneously, the first valve 72exhausts through the line 71, the opposite side of the cylinders 17, 18through the exhaust ports 74 or 75.

The pneumatic cylinder 43 is connected to a second control valve 76(preferably, identical to the first valve 72) that is operative to feedand exhaust said cylinder 43 through the transfer lines 77, 78. In otherwords, in the position shown in FIG. 1, spool element 79 connects feedconduit 73a to the transfer line 77 to cause piston 80 of the cylinder43 to be shifted to the right for the return stroke. At the same time,the spool element 79 exhausts the line 78 through exhaust port 81. Whenthe spool 79 of the second valve 76 is in the opposite position, asshown in FIG. la, the piston 80 is moved toward the fully extendedposition with the line 78 supplying the pressurized fluid and the line77 exhausting the fluid from the soft side by releasing the same throughexhaust port 82. The feed conduits 73a and 73 are provided withpressurized air from pressure source 85, and a separate air pressureregulator 86 is or may be provided along the conduit 73a in order toadjust the air pressure acting against the piston 80 to control forceand speed of the driving of the rollers 25, 26.

The valves 76 may include suitable electrical actuators, such assolenoids 90, 91, and in accordance with this invention, the solenoidsare controlled in synchronization by the central or master packagingmachine control 92. Feeding information to this control is aconventional photocell 93 that is operative to sense control marks onthe web W to designate the length of film to form the package P byopening of the sealing jaws 15, 16 at the proper instant. The signalfrom the photocell 93 is fed to the packaging machine control 92, andthis signal in turn, operates solenoid 90 to open the sealing jaws 15,16, as shown in FIG. 2, which is the end of the drawing stroke in theoperation.

The cutting loose of the package P and the opening of the sealing jawsl5, 16 preferably occurs before bottom dead center of the crank 20 forbuilt-in overtravel to assure full length drawing on each cycle (FIG.2). Similarly, the start of drawing film of FIG. 1 may be below top deadcenter to permit stripping (settling) of product into the package P, ifdesired.

OPERATION The basic overall operation of the above-described apparatusand the related method for unwinding the web roll R should now beevident to one skilled in the art, but it will be now reviewed tofurther bring out and emphasize the novel aspects of the invention. Thecarriage 19 of the device 10, which is in the preferred embodiment thepackage forming mechanism, is shown in FIG. 1 at the start of thedrawing stroke where the sealing jaws l5, 16 have finally closed andhave formed a transverse seal across the tube T. The crank 20 operatingfrom the main drive of the machine on a definite recurring cycle, startsthe downward motion of the carriage 19 to carry out this drawing step.

At this time, the rollers 51 of the dancer arm assembly are in theirlowermost position shown by the full lines of FIG. 1 with the brake shoe58 (and the brake shoe 57) in the fully applied condition. The piston ofthe cylinder 43 has moved the rack 40 into the fully retracted positionin standby for the forward drive of the rolls 25, 26. In this position,the web W is tensioned; however, since a portion of the weight of thedancer arm assembly is supported by the camming engagement at the camroller 56 (and roller 55), the tension is reduced even below theoperating minimum so that the web is not deleteriously stretched ordeformed even during shut-down periods that can be experienced with amachine between work shifts, for example.

As soon as the carriage 19 has moved a finite or predetermined distancedownwardly from the position shown in FIG. 1, the guide rollers 51 areraised, as shown by the arrows in FIG. 1. During this time, the brake isreleased so that the rolls 25, 26 are ready to be freely driven;however, the cylinder 43 is still retained in the standby or retractedposition.

As the guide rollers 51 are lifted from their lowermost position, thetension in the web is now determined solely by the weight of the dancerarm assembly pivoted about the pivot shaft 54. It is a desiratum of theinvention that this operating tension be maintained at a minimum and notvary by a significant amount. This is accomplished by marking thecomponents of a light material and/or providing counterbalancing weightat the rear of the dancer arm assembly; the tension thus being only thatnecessary to promote a wrinkle-free and non-sag condition. Also, thereis no spring urging 7 the assembly to the lowermost position, as iscommon on prior art devices.

With the drawing step reaching conclusion, the sealing jaws 15, 16approach their lowermost position and the photocell 93 senses thepackage length mark. At this moment, the sealing jaws 15, 16 arewithdrawn from their dotted line position to the full line position(FIG. 1a to release the tube T and to cause the package P that has beenpreviously cut to drop away in finished form. The photocell 93 hascaused this action through the master packaging machine control 92, thevalve 72 andits actuator 90. Concurrently, because of the directinterconnection of the actuator 91 with the actuator 90, the spoolelement 79 of the valve 76 is switched to the position shown in FIG. laand the piston 80 thus begins the drive motion. This is continued untilat the moment that the step of driving the roll R is finished, thedancer guide rollers 51 are at their lowermost position.

To further explain and to note the important braking operation, as therack 40 continues to drive the rollers 25, 26, the dancer guide rollers51 continue their downward movement toward the dotted line position ofFIG. 1a. Just before the rollers reach the rest position, the cam roller56 is brought into engagement with the leaf spring 67 (see FIG. 4) andthe application of braking force is begun. At this point, the rack 40has almost, but not completely, reached the end of its stroke. Thebraking force is rapidly, but smoothly applied until the point ofmaximum leverage engagement 69 (FIG. 1) is obtained between the leafspring 67 and the curved base 68. At this point, the support rollers 25,26 have been locked in position by the braking action and the pneumaticmotor or cylinder 43 has had its piston 80 stalled out. The pressureprovided through the regulator 86 is such that the compressible fluid onthe right of the piston 80 is not sufficient to overdrive theapplication of the brake 58.(and the brake 57 on the other side).Accordingly the feed of the web W stops at just the desired point, or inother'words, when the guide rollers 51 are in their dotted line position(FIG. 1a) at the lowermost point of travel.

When the carriage 19 has returned to its uppermost position by movingrelative to the tube T (see FIG. 1), the master packaging machinecontrol 92 through a suitable timing device, such as a cam, trips theactuator solenoids 90, 91 to bring the sealing jaws 15, 16 together forthe start of the next drawing stroke, and concurrently, quick returnsthe piston 80 and the drive rack 40 to the standby position in readinessfor the next cycle.

In summary, it can be seen that one of the salient features of theintermittent unwind method and apparatus of the present invention isthat the tension in the web is held at an operating minimum throughoutthe cycle. This is accomplished by initiating and performing the drivingoperation in response to an independent machine function, such as thecompletion of the drawing stoke, rather than in response to a designincrease in the tension, and stalling out the driving motor or cylinder43 of the web cradle 11. by a braking operation when the proper lengthhas been unwound from the roll R. For simplicity of control, theactuating means for the l I I sealing jaws 15, 16 of the packagingdevice 10 are directly interconnected with the actuating cylinder 43 ofthe roll cradle 11 causing the operations to be at mutually exclusivetimes; or in other words, each is operative 7 during the rest period ofthe other. Exact feeding of the web W is performed with ease since thedrive rack 40 has a built-in overrun that allows for at leastsomestalling period by the brakes during each cycle.

In this disclosure, there is shown and described only the preferredembodiment of the invention, but, as,

1. The method of cyclic or intermittent feeding and I unwinding of sheetmaterial from a web roll comprising the steps of intermittently drawinga predetermined 7 length of sheet material of said web roll supported onI spaced support rollers, intermittently directly driving said web rollthrough said support rollers to the final turn of said roll to unwind apredetermined length of 9 material substantially equal to that drawn andconcur rently forming a slack loop between said web roll and. said drawmeans varying from a minimum to a maxi-r I mum slack loop, said directdriving step being initiated and performed substantially independentlyof the tension in said web, whereby the tension in said web remains at aminimum and substantially constant as determined by the formation ofsaid slack loop and the} duration of the driving step is substantiallythe same during each cycle regardless of the diameter of the web roll.

2. The method of feeding and unwinding of claim '1 I I wherein thedrawing step and the driving step are at dif- I ferent times and thedriving step is terminated prior to said drawing step.

3. The method of feeding and unwinding of claim wherein the driving stepis commenced concurrently with the completion of the drawing step.

4. The method of feeding and unwinding of claim 1 wherein said drivingstep lasts longer than necessary to produce the predetermined length ofmaterial and braking is applied with respect to said roll to override Isaid driving to produce said predetermined length.

5. The method of feeding and unwinding of claim 1 wherein tension isplaced on said web in said slack loop that is limited to a valueinsufficient to unwind said material by itself.

6. The method of claim 1 wherein said maximum slack loop is provided atthe start of the drawing step and the minimum slack loop is provided atthe start of said driving step.

7. The method of claim 1 wherein is provided a pro- I gressive brakingof said web roll only during the final moments of unwinding, wherebyfree rotation at other 7 times allows minimum tension, and progressivelyreducing said tension further during braking to avoid stretching of saidmaterial during

1. The method of cyclic or intermittent feeding and unwinding of sheetmaterial from a web roll comprising the steps of intermittently drawinga predetermined length of sheet material of said web roll supported onspaced support rollers, intermittently directly driving said web rollthrough said support rollers to the final turn of said roll to unwind apredetermined length of material substantially equal to that drawn andconcurrently forming a slack loop between said web roll and said drawmeans varying from a minimum to a maximum slack loop, said directdriving step being initiated and performed substantially independentlyof the tension in said web, whereby the tension in said web remains at aminimum and substantially constant as determined by the formation ofsaid slack loop and the duration of the driving step is substantiallythe same during each cycle regardless of the diameter of the web roll.2. The method of feeding and unwinding of claim 1 wherein the drawingstep anD the driving step are at different times and the driving step isterminated prior to said drawing step.
 3. The method of feeding andunwinding of claim 2 wherein the driving step is commenced concurrentlywith the completion of the drawing step.
 4. The method of feeding andunwinding of claim 1 wherein said driving step lasts longer thannecessary to produce the predetermined length of material and braking isapplied with respect to said roll to override said driving to producesaid predetermined length.
 5. The method of feeding and unwinding ofclaim 1 wherein tension is placed on said web in said slack loop that islimited to a value insufficient to unwind said material by itself. 6.The method of claim 1 wherein said maximum slack loop is provided at thestart of the drawing step and the minimum slack loop is provided at thestart of said driving step.
 7. The method of claim 1 wherein is provideda progressive braking of said web roll only during the final moments ofunwinding, whereby free rotation at other times allows minimum tension,and progressively reducing said tension further during braking to avoidstretching of said material during down time.